1. Field of the Invention
The present invention generally relates to an air conditioning system and method for a vehicle, and more specifically, to an air-conditioning control of a vehicle which can heat and cool the air to be introduced into a passenger compartment by means of a temperature control unit so as to accomplish a desired temperature of a passenger compartment of a vehicle.
2. Related Art
Generally, in a vehicle equipped with an automatic temperature control system or a heater-air-conditioner system, a heat balance between a heat exchange capacity of the temperature control system and the heat load therefor is controlled to maintain a desirable temperature of the passenger compartment.
For example, the heat balance during cooling operation can be defined by the following equation: EQU Qa=Qu-Qs-Qm-Qe (1)
Wherein Qa is the heat-exchange capacity of the heater-air-conditioner system, Qu is a transmission loss due to the temperature difference between the ambient temperature and the passenger compartment temperature, Qs is a heat load caused by the solar radiation, Qm is a heat load dissipated from the human bodies of passengers, and Qe is a heat load dissipated from equipments in the vehicle, such as an internal-combustion engine. Further, Qa, Qu, Qs are given by the following equations: EQU Qa=Cp*.GAMMA.*Va(To-Tr) EQU Qu=K*A(Tr-Ta) EQU Qs=Ks*Ts
Wherein
Va:Outlet Air Volume of Blower (Delivery Air Volume of Blower); PA1 To:Outlet Air Temperature of Heater-Air-Conditioner System; PA1 Tr:Interior Temperature of Passenger Compartment PA1 Ta:Ambient Air Temperature (Outdoor Air Temperature) PA1 Ts:Reduced Temperature of Solar Radiation PA1 Cp:Specific Heat of Air at Constant Pressure PA1 .GAMMA.:Specific Gravity of Air PA1 K:Overall Heat Transfer Coefficient PA1 A:Heating Surface Area PA1 Ks:Conversion Coefficient for Converting Solar Radiation to Temperature.
In the above-mentioned formula (1), assuming Qm, Qe to be C(constant) since Qm and Qe can be considered as being approximately constant values, the equation (1) can be rewritten into the following equation: EQU Cp*.GAMMA.*Va(To-Tr)=K*A(Tr-Ta)-Ks*Ts-C (2)
If the interior temperature Tr is substantially equal to a preset temperature TSET which is manually set by the passenger, this equation can be further rewritten in to the following equation: EQU Cp*.GAMMA.*Va(To-TSET)=K*A(TSET-Ta)-Ks*Ts-C (3)
Thus, the desired values of the outlet air volume Va and the outlet air temperature To can be obtained from the above-mentioned equation (3) and the outlet air volume Va and the outlet air temperature To of the heater-air-conditioner system is converged to the desired values, respectively, whereby the interior temperature Tr can be maintained substantially at the preset temperature TSET. However, the above-mentioned equation includes two variables, that is, the outlet air volume Va and the outlet air temperature To, and therefore, it is difficult to obtain the really desired values of the volume Va and the temperature To directly or uniformly from the above equation (3).
In a heater-air-conditioner system disclosed in Japanese Patent Publication No. 62-8327 (Application No. 54-57215), the relationship between the outlet air volume and an environmental factor such as the ambient air temperature is predetermined, and the outlet air volume is determined in accordance with a detected environmental factor. Then, a desired outlet air temperature is computed from the determined outlet air volume, and the opening degree of an air-mixing door or damper is controlled so as to obtain the outlet air temperature.
Further, Japanese Patent Application Laid-Open Publication No. 57-77216 (Application No. 55-153718) discloses a heater-air-conditioner system in which an optimum outlet air temperature can be determined in accordance with a preset desired interior temperature, a detected ambient air temperature and a detected interior temperature.
In the system disclosed in the above-mentioned Japanese Publication No. 62-8327, and intended outlet air volume may be controlled, however the outlet air temperature is uncontrollable. On the contrary, according to the system disclosed in Japanese Laid-Open Publication No. 57-77216, an intended outlet air temperature may be controlled, but the outlet air volume is uncontrollable.
In particular, since a passenger in a vehicle tends to take a position relatively near to air outlets of a heater-air-conditioner system, an air flow of an excessively high or low outlet air temperature and/or an excessively high or low outlet air volume gives a discomfort the passengers, and therefore, such a system cannot meet passengers' requests for a comfortable air condition. Further, an effective temperature which a passenger feels relates to both the outlet air volume and the outlet air temperature. Where one of the outlet air volume and temperature is selected to be controlled and the other is left uncontrolled, the effective temperature would often come off from a desirable zone of the interior temperature.
The present inventors have already proposed a comfort index as a generic indication incorporating heating-air-conditioning factors such as the ambient air temperature, the interior temperature, and the solar radiation, and in Japanese Patent Application No. 3-170015, laid open to the public on May 14, 1993, which corresponds to the pending U.S. patent application Ser. No. 08/135,621, a vehicle air-conditioning system in which the operating conditions can be set in accordance with this comfort index. In this air-conditioning system, both of the outlet air temperature and the outlet air volume are determined so that the comfort index, which is set totally in consideration with various kinds of heating-air-conditioning factors, is controlled to a predetermined value. Then, a blower and a mixing door or damper in the air-conditioning system are controlled in order to regulate the outlet air temperature and the outlet air volume.
It should however be noted that the above proposed air conditioning system is disadvantageous in the following points. The target value of the comfort is fixed at a predetermined value. On the other hand, an effective comfort index which a passenger actually feels varies based on for example, the difference in individuals, climate and the like. Thus, the proposed system cannot reach the effective comfort which varies depending on the above factors and there is a need for a sophisticated air conditioning control.